When (meth)acrylic polymers having crosslinkable silyl groups at the termini are crosslinked, crosslinked materials having crosslinked sites at the termini of the polymers are produced as a result. Thus, (meth)acrylic polymers having crosslinkable silyl groups at the termini can be used to form elastic materials having large molecular weights between crosslinks.
These polymers can be used as highly weather-resistant materials and are particularly suitable for use in materials requiring rubber elasticity, such as sealants and adhesives.
Examples of methods for producing (meth)acrylic polymers having terminal crosslinkable silyl groups include a method disclosed in Japanese Examined Patent Application Publication No. 3-14068 in which a (meth)acrylic monomer is polymerized in the presence of a mercaptan containing a crosslinkable silyl group, a disulfide containing a crosslinkable silyl group, and a radical polymerization initiator containing a crosslinkable silyl group; and a method disclosed in Japanese Examined Patent Application Publication No. 4-55444 in which an acrylic monomer is polymerized in the presence of a hydrosilane compound containing a crosslinkable silyl group, or tetrahalosilane. Japanese Unexamined Patent Application Publication No. 6-211922 discloses a method for producing an acrylic polymer having terminal crosslinkable silyl groups, characterized in that a large amount of a hydroxyl-containing polysulfide relative to an initiator is used to synthesize an acrylic polymer having terminal hydroxyl groups, followed by conversion of the hydroxyl groups. Japanese Unexamined Patent Application Publication No. 5-97921 discloses a method for producing an acrylic polymer containing terminal crosslinkable silyl groups, including the steps of anionically polymerizing an acrylic monomer in the presence of a stabilized carbanion containing a crosslinkable silyl group and then reacting the termini of the polymer with a bifunctional electrophilic compound.
However, the above-described methods require particular functionalizing agents and thus have poor economic efficiency and problems relating to equipment. Moreover, in these methods, a heteroatom will be introduced into the polymer main chain skeleton. This is a problem since high heat resistance and high weather resistance of the (meth)acrylic polymer will no longer be achieved.
Atom transfer radical polymerization (hereinafter, ATRP), which is a type of living radical polymerization, is a useful method for producing (meth)acrylic polymers having functional groups (for example, refer to Matyjaszewski, et al., J. Am. Chem. Soc. 1995, vol. 117, p. 5614; Macromolecules, 1995, vol. 28, p. 7901, Science 1996, vol. 272, p. 866; and Sawamoto, et al., Macromolecules 1995, vol. 28, p. 1721). The ATRP may be employed to produce a (meth)acrylic polymer having terminal crosslinkable silyl groups. The present inventors have developed methods including the steps of preparing a halogen-terminated (meth)acrylic polymer by ATRP, converting the terminal halogen groups into alkenyl-containing substituents, and converting the alkenyl groups into substituents containing crosslinkable silyl groups (Japanese Unexamined Patent Application Publication Nos. 09-272714, 11-043512, 11-080250, and 2000-44626). Cured products having satisfactory characteristics can be produced by these methods since the functional groups can be reliably introduced to the termini of the polymers.
An example of a method for converting alkenyl groups into substituents containing crosslinkable silyl groups is hydrosilylation by which a hydrosilane compound containing a crosslinkable silyl group is added to the alkenyl groups. The hydrosilylation is preferably conducted in the presence of a transition metal complex functioning as a reaction catalyst to simplify the process.